This proposal describes experiments designed to identify and characterize Caenorhabditis elegans innate immune signaling pathways. During the past several years, my laboratory has pioneered the development of C. elegans pathogenicity models based on the observation that a remarkably large number of human pathogenic bacteria and yeasts kill C. elegans. Each of these pathogens has been studied by simply replacing C. elegans'normal food source (a lawn of Escherichia coli strain OP50) with a pathogen, and monitoring the survival of the nematodes overtime. This simple feeding-based pathogenicity model coupled with powerful genetic and genomic technologies, including RNAi feeding libraries, makes C. elegans an attractive model in which to dissect immune response signaling pathways. We have established that the C. elegans response to pathogen attack involves a conserved p38 MARK signaling pathway, a Toll-lnterleukin 1 Receptor (TIR)-domain-containing signaling component, programmed cell death, and antimicrobial effector proteins, all of which also function in mammalian innate immunity. Using both forward and reverse genetic approaches, we have identified at least six C. elegans genes (tir-1, nsy-1, sek-1, mek-1, vhp-1 and pmk-1) that function in a MARK innate immune signaling pathway homologous to the p38 MARK signaling pathway that functions in the mammalian innate immune response. We have also shown that the DAF-2 insulin-like signaling pathway plays a role in innate immune signaling. In preliminary data we have identified a variety of new genes that appear to encode additional components of the C. elegans PMK-1 (p38) signaling pathway as well as components of other immune pathways. We have also demonstrated that resistance to pathogenmediated killing can be independent of overall worm longevity. The specific aims are designed to further elucidate the role of the PMK-1 (p38) signaling pathway and other signaling pathways in activating the C. elegans immune response and to delineate the relationship between longevity and pathogen resistance.